A winder of the aforesaid kind, for instance for winding thread, yard, twist yarn, slit film or tape and the like, is expected to wind up the total delivered material completely and without delay. Owing to the fact that the amount of the supplied material is subject to great variations, manifested by a change of the thread tension, the rotatable speed of the take-up bobbin is in a generally-known manner readjustable by means of a thread tension regulating device, with the magnetic field between the motor-driven permanent magnet plate and the armature plate on the bobbin side being changed, whereby a more or less strong driving connection from the motor to the bobbin exists.
To change the magnetic field between the motor-driven permanent magnet plate and the armature plate at the bobbin side of the drive, it has been proposed to change the clearance between them. This, however, requires an axially displaceable positioning of either the driving motor or the winding arrangement, which is expensive.
Further, an arrangement of the aforesaid kind is known, wherein the two plates are arranged with a fixed axial distance to each other, with a shield of ferromagnetic material being pushed in the axial gap between these, thereby deflecting or shielding a part of the induced magnetic field.
Such an arrangement possesses considerable disadvantages, however, since the shield must be relatively thick so as not to bend under the effect of the magnetic field forces. This on the other hand requires a relatively wide air gap between the plates and relatively large permanent magnets to be able to generate a sufficient force field. This, however, increases the price of the whole arrangment not inconsiderably.